Watch a Water Droplet Wrap Itself in a Sheet of Plastic

Fluid dynamics is never not cool. Here we see ultra-thin sheets of polystyrene wrap themselves around shrinking water droplets.

At first it looks like the liquid water droplet in these videos is shrinking, or being compressed, by the thin sheet of material we can see across its surface. Actually, it’s being sucked down to size by a needle, but that doesn’t change the remarkable fact that, once it gets small enough, it wraps itself in that sheet of plastic. (Or that sheet wraps itself around the liquid, depending on how you look at it.)

How does this happen? Apparently at least a part is the power of thinness. Thicker sheets of liquid run into problems with capillary action—the result of molecules of water adhering to the material and then sticking together. With ultra-thin pieces of material, “interfacial energies and mechanical properties of the sheet are irrelevant,” and all the sheets, “achieve optimally efficient shapes that maximise the enclosed volume of liquid for a fixed area of sheet.” Make the sheet thin enough and it will perfectly wrap itself around anything without any complications.